Several intervention tools used in a well have an internal pump for providing fluid to an operational bit arranged in the front end of the tool. Thus, the pump needs a rotational input of a certain speed which is substantially higher than the rotational speed of the tool bit. The pump is therefore arranged so that fluid from the pump is supplied through a reduction gear, however, when intervening small diameter wells, this design is not appropriate as the reduction gear needs all the internal space available to avoid the gear being worn down very quickly.